1. Field of the Invention
The present invention relates to amplifier networks used in high frequency communication systems such as cellular communication systems.
2. Description of Prior Art
In communication systems, high frequency signals often require an increase in magnitude. This increase can be achieved by adding amplifiers designed for this purpose. These amplifiers are placed in series with the path of the signal. Two conditions that can affect the operation of the system employing these amplifiers are amplifier failure and the amplifier reaching its capacity limit.
An exemplary system employing high frequency amplification is a multi-sector cell within a cellular communication system. The most popular implementation of this type of system divides the cell into three sectors. These sectors are treated as independent paths for data traffic to follow. Data intended for radiation into the first sector is delivered to a first antenna through a first amplifier. Similarly, for paths 2 and 3, data intended for radiation into the second (third) sector is delivered to a second (third) antenna through a second (third) amplifier. The first, second and third amplifiers are also called Primary Amplifiers. In this system, if the first amplifier fails, the data cannot be delivered to the first antenna. The same is true for failure of the second amplifier or third amplifier, in the second and third paths, respectively.
A well known solution to this problem of an amplifier failure is to add an additional amplifier to the system. This amplifier is called an Auxiliary Amplifier. Such a network will be designed to allow the Auxiliary Amplifier to be switched into the position of any of the Primary Amplifiers while simultaneously switching out that primary amplifier. When a Primary Amplifier failure is detected, a command is sent to the network to switch in the Auxiliary Amplifier.
In one specific method of this solution of protecting against amplifier failure, a divider is used to split a signal into at least two paths, and a combiner to combine the at least two paths into a single transmission line. According to this method, each path has a primary amplifier, and each path has an auxiliary amplifier. The input to each auxiliary amplifier is normally shunted to ground through a switch, but in case a primary amplifier fails, the switch can be activated to shunt the failed amplifier's input to ground, which activates the auxiliary amplifier.
According to this method, multiple paths may be used to limit the effect of amplifier failure in any one path, but each auxiliary amplifier is associated with only one primary amplifier. Thus, a single auxiliary amplifier provides redundancy to only one primary amplifier and one signal path. Given the service reliability of amplifiers, it is inefficient to provide an auxiliary amplifier for each primary amplifier. In addition, it is occasionally useful to increase the amplifier capacity for a specific path by employing both a primary and auxiliary amplifier. This method does not allow the primary and auxiliary amplifiers to be employed together.
What is needed is an auxiliary amplifier circuit in which a single auxiliary amplifier can be switched to provide redundancy for a plurality of primary amplifiers.
What is also needed is an auxiliary amplifier circuit in which an auxiliary amplifier can cooperate with a primary amplifier to increase amplifier capacity for a circuit path.